The present invention relates to methods for building three-dimensional (3D) objects in extrusion-based digital manufacturing systems. In particular, the present invention relates to metallic modeling materials for use in extrusion-based digital manufacturing systems.
An extrusion-based digital manufacturing system (e.g., fused deposition modeling systems developed by Stratasys, Inc., Eden Prairie, Minn.) is used to build a 3D object from a computer-aided design (CAD) model in a layer-by-layer manner by extruding a flowable modeling material. The modeling material is extruded through an extrusion tip carried by an extrusion head, and is deposited as a sequence of roads on a substrate in an x-y plane. The extruded modeling material fuses to previously deposited modeling material, and solidifies upon a drop in temperature. The position of the extrusion head relative to the substrate is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D object resembling the CAD model.
Movement of the extrusion head with respect to the substrate is performed under computer control, in accordance with build data that represents the 3D object. The build data is obtained by initially slicing the CAD model of the 3D object into multiple horizontally sliced layers. Then, for each sliced layer, the host computer generates a build path for depositing roads of modeling material to form the 3D object.
In fabricating 3D objects by depositing layers of modeling material, supporting layers or structures are typically built underneath overhanging portions or in cavities of objects under construction, which are not supported by the modeling material itself. A support structure may be built utilizing the same deposition techniques by which the modeling material is deposited. The host computer generates additional geometry acting as a support structure for the overhanging or free-space segments of the 3D object being formed. Support material is then deposited from a second nozzle pursuant to the generated geometry during the build process. The support material adheres to the modeling material during fabrication, and is removable from the completed 3D object when the build process is complete.
A common interest of consumers in the industry of digital manufacturing is to increase the physical properties of the 3D objects, such as part strengths and durability. One category of materials that could provide such increased physical properties include metallic materials. For example, 3D objects built from steel may exhibit tensile strengths of about 480 megapascals (about 70,000 pounds/square-inch), which is substantially greater than those of industrial thermoplastic materials (e.g., about 30 megapascals (5,000 pounds/square-inch) for acrylonitrile-butadiene-styrene materials). However, the extrusion of metallic materials poses several issues for digital manufacturing. First, the extrusion of metallic materials require high operating temperatures, which may undesirably affect performance of the digital manufacturing systems. Furthermore, metallic materials typically exhibit substantial crystalline atomic-scale structures, which exhibit slushy states between their solidus and liquidus phases (for non-eutectic alloys) that may clog nozzles of the extrusion head. Thus, there is an ongoing need for materials that exhibit good physical properties and that are extrudable for use with digital manufacturing systems.